1. Field of the Invention:
The present invention relates to a recording apparatus such as a magnetic recording apparatus or an optical recording apparatus, each having airbearing head sliders (hereinafter simply referred to as a head slider). It relates, in particular, to an improvement in the mechanism for suspending the head slider (hereinafter referred to simply as a head suspension mechanism) which is moving over a rotating disk with a constant spacing therebetween, namely, with a constant flying height.
2. Description of the Prior Art:
As is widely known, in a magnetic or an optical recording apparatus, a magnetic or an optical transducer is mounted on an airbearing head slider which is flexibly supported by a suspension mechanism. Such a head suspension mechanism is required to have a rigid structure sufficient to stand the high speed accessing movement of the head slider and an adequate resilient mechanism to maintain a predetermined space between the rotating disk and the head slider flying over the disk.
The head suspension mechanism is secured to a rigid arm of a head actuator (a head positioner) which transfers the head slider in a substantially radial direction of the disk to access a track on the disk. The transducer is an electro-magnetic transducer or an optical head depending on the type of recording apparatus.
In order to make the head slider fly over the surface of a recording medium layer formed on a rotating disk with a predetermined spacing (hereinafter referred to as a flying height), the head slider is mounted on the free end of the head suspension mechanism, usually on the free end of a load beam.
With the above configuration, the head slider is pressed to the associated medium with a static load given by the head suspension mechanism when the disk is at rest. Hereinafter, the static load is referred to as "initial static load". The head slider is statically pressed against the disk when the head suspension mechanism is set in a predetermined position with respect to the medium, usually a medium layer formed on a rotating disk. With this configuration, a resilient section of the head suspension mechanism, namely a load beam, causes a resilient force which is applied to the head slider as an initial static load.
When the disk is rotating at a rotation speed such as 3600 rpm, the head slider flexibly supported by the head suspension mechanism, is subject to an aerodynamic lift force caused by the air flow generated by the rotation of the disk, and it floats over the surface of the disk.
The flying height of the head slider is determined by the balancing between the aerodynamic lift force and the initial static load. The aerodynamic lift force is determined by the surface circumferential speed of the associated medium disk in rotation. Consequently, the initial static load to be applied to the head slider, is approximately determined by the rotation speed and the radius of the disk, and the resilient characteristics of the head suspension mechanism.
The flying height is preferably small to achieve high resolution capability of the transducer, however, it is also preferably large in order to avoid contact of the transducer with the medium. As the recording density on the disk is increased, the flying height has been reduced down to a sub-micron range of less than 0.5 microns.
The setting accuracy of the initial static load depends on the accuracy of the associated mechanism, such as the load beam. Particularly, the resilient section of the load beam in the prior art has usually been subject to a plastic deformation during manufacture through which the section is formed in a curved shape to some degree. Precise operation to make the form in the resilient section is difficult since the load beam is made of spring material such as stainless steel. Inaccurate dimensions of the resilient section causes an undesirable initial static load. As a result, adjustment work to realize and maintain the flying height of the head slider over the disk within a required fluctuation limit, has been a very difficult and delicate matter. This has been an annoying problem requiring an extremely high accuracy in part fabricating work and the precise assembly of the head suspension mechanism. In order to overcome this problem, elaborate and time-consuming work has been inevitable for adjusting the already assembled head suspension mechanism to correct the flying height after assembling the head suspending mechanism.
Watraus, U.S. Pat. No. 4,167,765, discloses a transducer suspension mechanism having the above-described structure. In the side view shown in FIG. 2 of Watraus, a resilient spring section appears to be straight, thus the whole suspension element 10 appears to be flat. However, the resilient spring section 16 must have a form curving downward when the element 10 is considered as one of the parts of the apparatus, otherwise, the initial static load pressure toward the disk 24 can not be provided. Consequently, Watraus can not avoid the above-described problem.
In order to avoid the problem, it has been proposed to provide a variety of pressing members which engage a load beam to provide a pressure to the disk. The feature of these head suspension mechanisms commonly observed in these disclosures, is that the load beam mainly carries a head slider and a pressing member provides an initial static load to the head slider through the load beam. That is, the functions of carrying the head slider and of pressing the head slider, are separated, being individually assigned to different parts, a load beam and a pressing member.
Yamada, Japanese Patent Application No. 62-248178, published Oct. 29, 1987, has proposed an improved transducer suspension mechanism having the above-described feature. The head suspension mechanism of Yamada, as shown in FIG. 1 and FIG. 2 of the disclosure, has an appearance similar to that of Watraus except for a pressing member comprising a supporting arm 31 and a pressing spring 40 which is secured to the free end of the arm 31. The pressing spring 40 directly presses the relevant head slider 50 from the backside thereof through a protuberance 25. The advantage of this configuration lies in that the resilient section 18 is flat and needs not be subject to plastic deformation in order to be formed in a curved or a cylindrical plane, thus being free from the above-described difficulty. However, the load provided by the pressing spring directly applied to the head slider, is required to have the same order of accuracy as that required for the head slider. This still causes an accuracy problem in the formation of the spring 40 and the setting of the pressing member.
Meanwhile, Mizoshita, a co-inventor of the present invention, has also disclosed another improved transducer suspension mechanism in Unexamined Japanese Patent Application No. 61-273783, published Dec. 4, 1986. As shown in FIG. 1 and FIG. 2 of the disclosure, an auxiliary spring 21 having a frictional protuberance 22 is disposed to press a rigid section of a load beam through the protuberance 22. A resilient section 2 of the load beam is formed to have a curved plane as that of Watraus, and pressure imposed on a head slider 4 is the resultant of pressures caused by the resilient portion 2 and the spring 21. The most favorable advantage of Mizoshita is a damping function to the mechanical oscillation which is caused by quick stop and start movements of the head slider under accessing operation. According to the disclosure, mechanical vibration of the load beam is damped by the friction between the surface of the rigid section of the load beam and the frictional protuberance 22 both of which are moving in a mutual rubbing motion.
Because of the severe requirement for the pressure loaded on a head slider, an adjustment means for the load is desirable. The adjusting means is found, for example, in Unexamined Japanese Patent Application No. 63-188856, published on Aug. 4, 1988, invented by Kuzuhara. However, the disclosure relates to a head suspension mechanism of a magnetic head recording apparatus employing floppy disks, wherein magnetic heads are not of the floating type, often being in contact with surfaces of the floppy disks. Magnetic heads, as shown in FIG. 1 of the disclosure, are pressed against a floppy disk 24 through a gimbal plate 12, spring plate 16, and an adjusting spring 17 the pressure of which is adjusted by an adjusting screw 20.